Using in vivo techniques, we proposed to determine the incidence of 1,2-dimethylhydrizine (DMH)-induced colon cancer in DB-IX and DB-II rats of different ages and also to measure early changes in the proliferation of colonic cells after the administration of DMH. In addition, the effect of gonadectomy on DMH-induced colon cancer in young and old rats will be determined. We will then attempt to determine the effects of gonadal hormone treatment prior to and during DMH administration on the initiation and/or growth of colon cancer in gonadectomized rats. Investigations will be made to determine the effect of DMH on the incidence of colon tumors induced transplacentally and whether gonadal hormones influence the induction in gonadectomized rats.